Exploded biomass based slow-release fertilizer

ABSTRACT

A fertilizer product comprising an acid-carbonized microporous matrix derived from expanded biomass and a fertilizer reaction product of residual acid from the carbonizing process and at least one added fertilizer precursor. The biomass may include steam exploded wood powder. The expanded biomass may be carbonized with a combination of sulphuric and phosphoric acids, followed by ammoniation to produce ammonium sulphate and mono- or diammonium phosphate. The fertilizer reaction product adsorbs onto the carbon matrix, which results in a slow-release when the material is applied to the soil.

FIELD OF THE INVENTION

The present invention relates to a novel slow-release fertilizerproduced from exploded biomass, and methods for producing the same.

BACKGROUND

Many techniques have been developed for delivering nutrients to growingplants and for extending or delaying the release of nutrients from afertilizer. Fertilizer is often applied to the ground as a formulatedsolid granule or powder, or as a liquid.

There are basically two types of fertilizers, water-soluble fertilizersand “slow-release” fertilizers. While water-soluble fertilizers aregenerally less expensive than slow-release fertilizers, they have thedisadvantage of leaching nutrients very quickly into and through thesoil. Slow-release fertilizers are designed to release nutrients toplants or soil over an extended period of time, which is more efficientthan multiple applications of water-soluble fertilizers. Therefore,slow-release (also referred to as controlled release or extendedrelease) fertilizers minimize the frequency with which plants must befertilized, as well as reduce or minimize leaching. The major advantageof slow release fertilizers is the optimal release and absorption of thecrop input nutrient by the roots along the period of growth, thusminimizing wastage of the nutrient and delivering better economic value.

Some solid, water-soluble fertilizers can be converted into slow-releasefertilizers by employing various coatings. Also, some polymers may bindprimary nutrients such as nitrogen in an insoluble form. Polymercoatings such as urea-formaldehyde (UF) condensation products such aspolyurethane are widely used as slow-release nitrogen fertilizers forcrops, ornamental plants and grasses. Urea-formaldehyde fertilizermaterials also can be supplied either as liquids or as solids. Suchmaterials generally contain at least 28% nitrogen, largely in awater-insoluble, slowly available form.

Extended release UF fertilizers may be prepared by reacting urea andformaldehyde at an elevated temperature in an alkaline solution toproduce methylol ureas. The methylol ureas then are acidified topolymerize the methylol ureas to methylene ureas, which increase inchain length as the reaction is allowed to continue. These methyleneurea polymers normally have limited water solubility, and, thus, releasenitrogen throughout an extended period. Such UF fertilizers usuallyinclude a mixture of methylene urea polymers generally have a range ofmolecular weights and are understood to be degraded slowly by microbialaction into water-soluble nitrogen. UF fertilizers are usuallycategorized by the amount and the release characteristics of their waterinsoluble nitrogen.

Polymer coated slow-release fertilizers suffer from certaindisadvantages. The polymer shell may crack or be damaged duringtransportation and handling, resulting in unrestricted moisture ingressand loss of slow-release ability. The polymer shells are often poorlybiodegradable, and build up in the soil after repeated use.

Granular nitrogen-containing fertilizers have been produced commerciallyby a variety of techniques using water-soluble nitrogen products, suchas urea, potassium nitrate, and ammonium phosphate. The practicaladvantages of handling, blending, and storing such fertilizer granulesare known and well documented. The preparation of granular fertilizersusing slow-release UF fertilizers also has been described in the priorart.

Nitrogen fertilizer comprising ammonium salts may be produced byabsorbing ammonia with an acid. However, uncoated slow-releaseformulations of such soluble nitrogen fertilizers are not known.

SUMMARY OF THE INVENTION

In general terms, the invention comprises a slow-release fertilizerproduct comprising an acid-carbonized microporous matrix formed from anexpanded biomass, and a fertilizer reaction-product of residual acidfrom the carbonizing process and at least one added fertilizerprecursor. The biomass may comprise fibrous lignocellulosic biomass,which is expanded or defribrillated to create a structure which becomesmicroporous upon carbonization, and which comprises exposed lignin. Inone embodiment, the biomass is defibrillated by gas-expansion, thermal,mechanical or chemical means. In one embodiment, the biomass is expandedusing steam explosion, supercritical gas expansion, or thermomechanicalmethods.

In one embodiment, the expanded biomass is carbonized with sulphuricacid, or phosphoric acid, or a combination of sulphuric and phosphoricacids. The carbonization process results in some residual acid embeddedin the pore volume of the microporous structure, however, in oneembodiment, the amount of acid used is controlled so as to avoidsaturating the pore volume. A liquid fertilizer precursor may then beadded to the pore volume, resulting in reactions with the residual acidand the creation of fertilizer products within the pore volume.

If the expanded biomass is carbonized with sulphuric acid, phosphoricacid may be added as a fertilizer precursor, followed by exposure toammonia, in either gas or liquid form. The resulting fertilizer productscomprise ammonium sulphate from the reaction between ammonia andresidual sulphuric acid, and mono or diammonium phosphate from thereaction between ammonia and the phosphoric acid.

In another embodiment, the added fertilizer precursor comprisespotassium hydroxide, which will react with residual sulphuric acid toform potassium sulphate. Additional sulphuric acid may be added to reactwith any excess potassium hydroxide to form additional potassiumsulphate.

If the expanded biomass is carbonized with sulphuric acid, a portion ofthe sulphuric acid may react with the lignin exposed during the biomassexpansion process, to form lignosulphonates. The amount of sulphuricacid may be controlled to substantially carbonize the expanded biomass,react with lignin to form lignosulphonates, and leave some residualsulphuric acid in the pore volume of the carbonized microporous matrixfor subsequent fertilizer forming reactions.

Therefore, in one aspect, the invention comprises a slow-releasefertilizer product comprising an acid-carbonized microporous matrixderived from expanded biomass and a fertilizer reaction-product ofresidual acid from the carbonizing process and at least one addedfertilizer precursor.

In one embodiment, the fertilizer precursor comprises one or more ofadditional sulphuric acid, phosphoric acid, nitric acid, potassiumhydroxide, ammonia, sulphur dioxide, or hydrogen sulphide. The productmay further comprise a micronutrient, which may comprise Mg, Cu, Zn, Fe,B, Mn, or Mo.

In another aspect, the invention may comprise a method of forming aslow-release fertilizer product, comprising the steps of:

-   -   (a) carbonizing an expanded biomass material with either or both        sulphuric acid and phosphoric acid to form a microporous carbon        matrix, leaving residual acid in the pore volume; and    -   (b) adding a fertilizer precursor to react with the residual        acid to form a fertilizer.

In one embodiment, the amount of acid is selected so as to leave openpore volme after carbonization. The fertilizer precursor may be a gas orliquid and added to the open pore volume. In one embodiment, the biomassis expanded prior to carbonization by steam explosion.

In another aspect, the invention may comprise an intermediate productfor producing a fertilizer product, comprising:

-   -   (a) an acid-carbonized microporous matrix derived from expanded        biomass, having an available pore volume; and    -   (b) a residual acid from the carbonizing process impregnated in        the pore volume, in an amount less than 71% by weight of the        intermediate product, and/or less than about 80% of the        available pore volume.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to a novel slow-release fertilizerproduced from expanded fibrous lignocellulosic biomass materials. Thebiomass is expanded by means of using expansion techniques such as steamexplosion or mechanical defibrillation. As used herein, “expandedfibrous lignocellulosic biomass” means fibrous lignocellulosic biomasswhich has been expanded so as to disrupt the fibrous structure, anddisrupt or destroy cell wall structures, thereby creating a microporousmatrix and increasing the available surface area for reaction. As usedherein, a slow- or controlled-release fertilizer is a fertilizercontaining a plant nutrient in a form which delays its availability forplant uptake and use after application, or which extends itsavailability to the plant significantly longer than a reference ‘rapidlyavailable nutrient fertilizer’ such as ammonium nitrate or urea,ammonium phosphate or potassium chloride. Such delay of initialavailability or extended time of continued availability may occur by avariety of mechanisms. These include controlled water solubility of thematerial by semi-permeable coatings, occlusion, protein materials, orother chemical forms, by slow hydrolysis of water-soluble low molecularweight compounds, or by other unknown means. Without restriction to atheory, the slow-release fertilizers of the present invention rely onthe adsorption of fertilizer onto a microporous carbon matrix.

The process of expansion of the biomass may result in increased porevolume and/or surface area. As used herein, pore volume means a measureof the void (i.e., “empty”) spaces in a material, and is conventionallyexpressed as a fraction of the volume of voids over the total volume,between 0 and 1, or as a percentage between 0 and 100%.

In one embodiment, the fibrous lignocellulosic biomass comprisesmaterial such as wood chips or wood particles, sugarcane bagasse, cerealstraw, corn stover, and other similar material. In one preferredembodiment, the biomass may comprise a wood powder, such as a softwoodsuch as pine, formed by grinding or pulverizing wood chips to particlesizes in the range of about 100 microns to about 500 microns.

Lignocellulosic fibers are a cellular composite material comprisinglignin, cellulose and hemicelluloses. The cell walls are formed fromcellulose microfibrils embedded in a matrix of hemiceullulose andlignin. Cellulose microfibrils are composed of cellulose assembled intolong overlapping parallel arrays a few nanometers in diameter. Therigidity and orientation of these microfibrils control cell expansion.Hemicellulose is a branched heteropolymer polysaccharide with a random,amorphous structure with little strength.

Lignin is a complex network of phenolic compounds found in secondarycell walls of woody tissues, and occupies the interstices between othercell wall components making the walls rigid and permanent

Expansion of the fibers, such as by steam explosion, results in theopening up of the fiber and complete or partial destruction of the cellwalls. Both steam and acetic acid, which is released from the biomassduring steam explosion, trigger the hydrolysis of hemicelluloses. Thelignin becomes exposed on the surface of the cellulose microfibrils, andas a result, the exposed lignin is more readily available for in-situreactions. There is a significant increase in porosity and surface areaof the expanded biomass. The bulk density of the biomass may decrease bygreater than about 30%, 50%, 100%, 200%, or 300%.

Expansion of the biomass in this context is largely similar topretreatment of biomass in the field of biofuel production. The goal isto greatly increase the surface area of the biomass, thereby increasingthe susceptibility of the biomass to chemical modification, forsubsequent processing steps. Various pre-treatments are surveyed inAgbor et al, “Biomass Pretreatment: Fundamentals toward Application”,Biotech. Advances 29 (2011) 675-685, the entire contents of which areincorporated herein by reference, where permitted.

Expansion may be accomplished by a hydrothermal process such as steamexplosion, which is a known process to those skilled in the art. Steamexplosion is a process in which biomass is treated with hot steam (180°to 240° C) under pressure (1 to 8 MPa) followed by an explosivedecompression of the biomass that results in a rupture of the biomassfibres rigid structure. The sudden pressure release defibrillates thecellulose bundles resulting in exposure of ruptured cells pore volume.

Generally there are several, commercially-available steam explosionprocesses. In one example, a two-step process is generally used wherethe material is first heated with lower pressure steam to preheat thebiomass, vaporize any residual water and open the pore structure. Thispreheated material is then pressurized with high pressure steam andsoaked for a prescribed period of time and then rapidly depressurized toexplosively release the steam from the pores of the biomass. The fibersof the biomass substantially disassociate, resulting in an expandedmicroporous material. In alternative process, the biomass may betransported with an auger rotating within a sealed cylinder, andpressurized with steam at various points along the auger. In some ofthese apparatuses, the seal for the steam pressure is provided by abiomass plug and in others by periodic lock-hoppers. Conventional steamexplosion is accomplished with steam pressure of from about 200 to about1000 psig (1.4 MPa to 6.9 MPa) and soak times from about 2 seconds toseveral minutes. The higher the temperature and pressure, and the longerthe soak time, the more complete the fragmentation of the biomass is.

The severity index of a steam explosion treatment (R_(o)) is a functionof reaction time (t) and temperature (T) according to the followingequation (Overend and Chornet, 1987)

$R_{o} = {\int_{0}^{t}{{\exp( \frac{( {T - 100} )}{14.75} )}{dt}}}$

Biomass destruction begins at about 2.0 on this index. With highseverity treatments (R_(o)>4), dehydration and condensation reactionsmay occur, and sugars may be degraded. In one embodiment, the expandedbiomass is created by a treatment with a severity index greater thanabout 2.0, preferably greater than about 3.0, and more preferablygreater than about 4.0.

Mechanical, thermal and/or chemical defibrillation techniques are knownand may also be used to produce the expanded biomass. For example, woodmay be subjected to grinding and refining steps, similar to those usedto produce mechanical pulp. Mechanical defibrillation may be also beused as a pre-treatment step for steam explosion.

In a preferred embodiment, the biomass is expanded by steam explosion.Without restriction to a theory, the use of steam explosion may leavethe expanded biomass saturated with steam that will condense if thebiomass is immediately quenched with acid at a lower temperature. Theexpanded biomass saturated with steam will generally come out of thesteam explosion process at about 120° C.-200° C. As the condensation ofsteam will create a vacuum, the acid may be quickly drawn into the poreswhile it is still concentrated, prior to becoming diluted by dehydrationreactions at the surface of the biomass particle. Because of thisinduction of the acid into the microporous structure of the explodedbiomass, less acid may be necessary to complete the carbonization. Thissame effect can be realized by high-pressure steaming of the biomasseven after it has been mechanically expanded, so the mechanism can beused on any type of exploded or ground biomass. Alternatively, the steamexploded biomass may be allowed to cool and/or dry before acidcarbonization.

The acid-carbonized microporous matrix is created when expanded biomasssource is dehydrated by treatment with a mineral acid or blend ofmineral acids. For example, cellulose decomposes to carbon and water:

(C₆H₁₀O₅)n+sulphuric acid 6_(n)C+5_(n)H₂O

Hemicellulose is also dehydrated to a carbon. Wihtout restriction to atheory, the reduction in hemicellulose caused by a steam explosiontreatment means that less acid is consumed by dehydratinghemicelluloses, as compared with non-expanded biomass.

The reaction of the exploded biomass with acid can include theintroduction of sulphuric acid to carbonize the expanded biomass inorder to create a microporous carbon matrix which will serve as the slowrelease carrier for the end fertilizer product. The quantity ofsulphuric acid will be chosen to substantially carbonize the expandedbiomass, preferably without saturating the pore volume. The goal is toleave sufficient pore space to add at least one additional fertilizerprecursor to the pore structure, which may be subsequently converted toa fertilizer product. In one embodiment, the amount of acid to carbonizethe biomass may be determined which will leave approximately half thepore volume filled with residual acid. A volume of liquid fertilizerprecursor may then be chosen to completely react with the acid and formthe desired fertilizer reaction product.

The carbonization of biomass with sulphuric acid conventionally requiresan excess of sulphuric acid. For example, in Applicant's co-owned U.S.Pat. No. 8,198,211, weight ratios of greater than 1:1, in the range of2.5:1 (250%) to 4.5:1 (450%) of acid to biomass were used, whichresulted in complete carbonization, and retention and impregnation ofresidual excess acid. In embodiments of the present invention,significantly less sulphuric acid may still result in substantial orcomplete carbonization of the expanded biomass, with an amount ofresidual acid in the pore volume still present and available forconversion to a fertilizer.

In one embodiment, the exploded biomass may be carbonized with sulphuricacid, which may be 40% to 100% concentrated sulphuric acid (by massfraction), preferably 50% to 100%, and more preferably 75 to 100%. Inone embodiment, the biomass material is carbonized with a quantity ofsulphuric acid in the range of about 0.25% to about 200% by weight. Inone embodiment, the ratio of sulphuric acid is less than 100% of theexpanded biomass by weight, preferably in the range of about 25% toabout 99%, depending on the characteristics of the biomass, the severityof the biomass expansion treatment, the concentration of sulphuric acidused, and the amount of residual sulphuric acid desired.

In another embodiment, the expanded biomass may be carbonized with acombination of sulphuric acid and phosphoric acid. As the two acids donot react with each other, each will participate in the carbonization ofthe expanded biomass and remain in residual quantities in the porevolume of the carbonized expanded biomass. As sulphuric acid is morereactive than phosphoric acid, it is likely that more sulphuric acidthan phosphoric acid will be consumed in the dehydration reactionsduring carbonization. However, both acids will be drawn into the porevolume of the expanded biomass, as discussed above.

In another embodiment, the expanded biomass may be carbonized withliquid phosphoric acid. Phosphoric acid melts at about 42° C., and has adensity of about 1.89 g/ml as a liquid. To accelerate the carbonizationprocess, it is preferred to preheat the phosphoric acid before additionto the expanded biomass. In one embodiment, the phosphoric acid ispreheated to about 100° C. to about 180° C. As such, the phosphoric acidis less dense and viscous, which may allow better penetration of thepore volume.

Phosphoric acid may be used as concentrated acid, or as a solution of atleast 50% acid (by mass fraction), and more preferably at least 75%. Inone embodiment, the biomass material is carbonized with a quantity ofphosphoric acid in the range of about 100% to about 300% by weight ofthe biomass. In one embodiment, the ratio of phosphoric acid is lessthan 300% of the expanded biomass by weight, preferably in the range ofabout 200% to about 250%, depending on the characteristics of thebiomass, the severity of the biomass expansion treatment, the moisturecontent of the biomass, the concentration of phosphoric acid used, andthe amount of residual acid desired.

In the carbonization step, substantially complete carbonization of theexpanded biomass is achieved in a reasonable time period, resulting in amicroporous carbonized matrix, with acid embedded in the available porevolume. This intermediate product is converted to a fertilizer productin a subsequent step. The rate of carbonization is aided by theincreased surface area of the expanded biomass. Therefore, the amount ofacid required may depend on the severity of the biomass expansion methodused and/or the size of the expanded biomass particles. For example, ifwood particles after steam explosion have a particle size less than 16mesh (<1.19 mm), an acid:wood weight ratio of about 1:1 or less (usingconcentrated sulphuric acid) may be sufficient to completely carbonizethe expanded wood particle. An amount of residual sulphuric acid may bepresent, but saturation of the pore volume of the carbonized expandedbiomass matrix is avoided.

The intermediate product for producing a fertilizer product maytherefore comprise:

-   -   (a) an acid-carbonized microporous matrix derived from expanded        biomass, having an available pore volume; and    -   (b) a residual acid from the carbonizing process impregnated in        the pore volume, in an amount less than 71% by weight of the        intermediate product, or less than 80% of the available pore        volume.

In one embodiment, the residual acid comprises less than about 60%,preferably less than about 50%, and more preferably less than about 40%by weight. By another measure, the residual acid occupies less thanabout 80%, preferably less than about 70%, more preferably less thanabout 60% of the available pore volume.

The process of biomass expansion exposes lignin. Without restriction toa theory, a portion of the added sulphuric acid during carbonizationreacts with the exposed lignin to form lignosulphonates, which aresulphonated lignin polymers. The resulting lignosulphonates may havevery broad distribution of molecular weights, which may depend on theseverity of the biomass expansion methods used. The conversion of ligninto lignosulphonate can be controlled by varying the quantity of acid andthe process conditions, i.e. the bed temperature. A slight excess ofacid may promote the formation of lignosulphonates. Lignosulphonates areknown binders used in the formation of fertilizer pellets. As a result,the resulting particles may be formed into pellets without addedbinders, or with reduced binder requirements.

The sulphuric acid and/or phosphoric acid laden carbonized matrix maythen be reacted with other chemicals, such as ammonia. The open porespace in the microporous carbon matrix allows the addition of a liquidfertilizer precursor to form fertilizer products. In one embodiment, ifsulphuric acid alone was used for carbonization, an amount of phosphoricacid may be added. The residual sulphuric acid and the added phosphoricacid do not react with each other and hence they remain as such. Thisintermediate product may then be reacted with ammonia, in either liquidor gas form.

The introduced ammonia will react with the different acid components toform different compounds. For example, in the case of a carbon matrixthat contains a mixture of sulphuric acid and phosphoric acid, thesulphuric acid will react with the ammonia to form ammonium sulphate andthe phosphoric acid will react with the ammonia to form mono ordiammonium phosphate. Both reactions are spontaneous and the resultingproduct will contain varying amounts of each compound depending on theratios of acid present in the biomass micro-pores. The formation of monoor diammonium phosphate can be controlled by varying the quantity ofammonia injected into the reaction bed and different compounds can beproduced by the use of different acids.

The resulting ammonium sulphate will be acidic of its own accord (saltof a strong acid and weak base). Advantageously, in the presence of anacidic fertilizer compound, the phosphate may be more available forplant nutrition by making it less susceptible to precipitation tocalcium or iron phosphates in the soil. Calcium present in the soil willdiffuse into the carbon pores at only a very slow rate, preserving thephosphates and sulphates contained there for plant nutrition.

In another embodiment, other basic compounds may be added to react withthe residual acid, to create fertilizer products. For example, anaqueous solution of potassium hydroxide may be added as a fertilizerprecursor, which will react with residual sulphuric acid in themicroporous matrix, to form potassium sulphate and water. These andother examples of added fertilizer precursors, and resulting fertilizerproducts may be seen in the following table:

Chemical Compound Formed Sulphuric Acid Ammonium Sulphate with AmmoniaPhosphoric Acid Ammonium Phosphate with Ammonia Nitric Acid AmmoniumNitrate with Ammonia Potassium Hydroxide Potassium Sulphate withSulphuric Acid Potassium Hydroxide Potassium Nitrate with Nitric AcidPotassium Hydroxide Potassium Phosphate with Phosphoric Acid AmmoniaAmmonium phosophate, Ammonium sulphate, ammonium nitrate Sulphur DioxidePotassium Sulphite with Potassium Hydroxide Hydrogen Sulphide PotassiumSulphide with Potassium Hydroxide

In addition, if desired, micronutrients may be added, in the form oftheir available salts, such as one or more of Mg, Cu, Zn, Fe, B, Mn, andMo.

The resulting particles then comprise the microporous carbon matrix,loaded with the fertilizer reaction products in the pore volume, andoptional micronutrients, and may include exposed lignosulphonates. Theparticles may then be blended with additional binders and water ifnecessary, and either granulated using traditional granulationtechniques or pelletized using any commonly available pellet mills. Anyother beneficial salt or mineral could be added to improve the nutritivevalue of the fertilizer product. The granulated or pelletized product isthen dried using commonly known methods following which it is cooledand, optionally, a coating may be applied to prevent dusting and improvestorage properties.The resulting products can be used as fertilizers forenhancing the growth of plants. The carbon in the carbonized microporousmatrix may act as an exchange substrate so that when water is introducedand the salt compounds dissociate, the carbon binds to the resultinganions and cations, resulting in a slow release over an extended periodof time. Therefore, the products may have utility as slow-releaseproduct of water soluble fertilizer compounds.

Excess acid and fertilizer precursors may be used to form fertilizerwhich will be associated with the microporous carbon matrix, but notadsorbed on the carbon matrix. Thus, a proportion of the fertilizerproducts may be immediately available from the pore volume, whileanother portion will be bound and be slowly released. The proportionbetween immediately available and slowly released fertilizer may becontrolled by varying the excess amount of acid and fertilizer precursormaterial.

EXAMPLES Example 1

As a first step, biomass in the form of pine wood powder (size rangeapproximately 100-500 microns with a moisture content of about 6% byweight) is steam exploded by soaking in steam at 220° C. at 3 MPa,followed by explosive decompression. The material is observed to expandin volume by about 30%. 1 kg of expanded biomass is treated with 2.86 kgof concentrated sulphuric acid (93% by mass fraction) to producemicroporous carbon matrix. No heating is required, as this reaction isexothermic and hence it proceeds with liberation of heat which willraise the biomass temperature to 100-180° deg C. 2.86 kg of concentratedphosphoric acid (93% by mass fraction) is then added to further fullyimpregnate the carbon alongside sulphuric acid which is alreadypartially present in the pores from the first step. The phosphoric acidmay be preheated to about 150° C. The higher bed temperature helpsreduce the density and viscosity of the phosphoric acid which allows itto diffuse and penetrate deep into the pores of the carbon matrix toyield an intermediate product. The resulting intermediate product isammoniated using 1.82 kg of gaseous anhydrous ammonia to yield 7.71 kgof ammonium sulphate and diammonium phosphate product adsorbed in thecarbon matrix. The ratio of ammonium sulphate and ammonium phosphate canbe varied by controlling the quantity of sulphuric acid added in thefirst step and the quantity of phosphoric acid added in the second step.

In another example, 1 kg of expanded biomass on a dry weight basis istreated in one single step with 5.72 kg of a blend of equal amounts ofsulphuric acid and phosphoric acid (each 93%). Sulphuric acid andphosphoric acid do not react with each other and on such treatment thesulphuric acid being the stronger hygroscopic acid, will react firstwith the biomass converting it to microporous carbon matrix which willthen allow the phosphoric acid as well to diffuse into the porestructure of the carbon matrix along with sulphuric acid. Thus, anintermediate product is formed with a carbon matrix impregnated with acombination of sulphuric acid and phosphoric acid. The intermediateproduct is then ammoniated to obtain a slow release fertilizerconsisting of ammonium sulphate and ammonium phosphate in a carbonmatrix.

Example 2

1 kg of expanded biomass as in Example 1 is reacted with 5.72 kg ofconcentrated phosphoric acid (93%) to convert the biomass to carbon. Thephosphoric acid is preheated to 150° C. The heat also helps in reducingthe density and viscosity of phosphoric acid aiding in better diffusioninto the micro pores of the carbon matrix. This intermediate product(phosphoric acid impregnated carbon matrix) is ammoniated with 1.82 kgof anhydrous ammonia to yield 7.71 Kg of diammonium phosphate product.

Example 3

1 kg of intermediate product formed in Example 2 above is reacted with9.75 kg potassium hydroxide (in aqueous solution) to yield 14.95 kg oftripotassium phosphate.

INTERPRETATION AND DEFINITION

The description of the present invention has been presented for purposesof illustration and description, but it is not intended to be exhaustiveor limited to the invention in the form disclosed. Many modificationsand variations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention.Embodiments were chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The corresponding structures, materials, acts, and equivalents of allmeans or steps plus function elements in the claims appended to thisspecification are intended to include any structure, material, or actfor performing the function in combination with other claimed elementsas specifically claimed.

References in the specification to “one embodiment”, “an embodiment”,etc., indicate that the embodiment described may include a particularaspect, feature, structure, or characteristic, but not every embodimentnecessarily includes that aspect, feature, structure, or characteristic.Moreover, such phrases may, but do not necessarily, refer to the sameembodiment referred to in other portions of the specification. Further,when a particular aspect, feature, structure, or characteristic isdescribed in connection with an embodiment, it is within the knowledgeof one skilled in the art to affect or connect such aspect, feature,structure, or characteristic with other embodiments, whether or notexplicitly described. In other words, any element or feature may becombined with any other element or feature in different embodiments,unless there is an obvious or inherent incompatibility between the two,or it is specifically excluded.

It is further noted that the claims may be drafted to exclude anyoptional element. As such, this statement is intended to serve asantecedent basis for the use of exclusive terminology, such as “solely,”“only,” and the like, in connection with the recitation of claimelements or use of a “negative” limitation. The terms “preferably,”“preferred,” “prefer,” “optionally,” “may,” and similar terms are usedto indicate that an item, condition or step being referred to is anoptional (not required) feature of the invention.

The singular forms “a,” “an,” and “the” include the plural referenceunless the context clearly dictates otherwise. The term “and/or” meansany one of the items, any combination of the items, or all of the itemswith which this term is associated. The phrase “one or more” is readilyunderstood by one of skill in the art, particularly when read in contextof its usage.

As will be understood by one skilled in the art, for any and allpurposes, particularly in terms of providing a written description, allranges recited herein also encompass any and all possible sub-ranges andcombinations of sub-ranges thereof, as well as the individual valuesmaking up the range, particularly integer values. A recited range (e.g.,weight percents or carbon groups) includes each specific value, integer,decimal, or identity within the range. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths, ortenths. As a non-limiting example, each range discussed herein can bereadily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art, all languagesuch as “up to”, “at least”, “greater than”, “less than”, “more than”,“or more”, and the like, include the number recited and such terms referto ranges that can be subsequently broken down into sub-ranges asdiscussed above. In the same manner, all ratios recited herein alsoinclude all sub-ratios falling within the broader ratio.

The term “about” can refer to a variation of ±5%, ±10%, ±20%, or ±25% ofthe value specified. For example, “about 50” percent can in someembodiments carry a variation from 45 to 55 percent. For integer ranges,the term “about” can include one or two integers greater than and/orless than a recited integer at each end of the range. Unless indicatedotherwise herein, the term “about” is intended to include values andranges proximate to the recited range that are equivalent in terms ofthe functionality of the composition, or the embodiment.

What is claimed is:
 1. A fertilizer product comprising anacid-carbonized microporous matrix derived from expanded biomass and afertilizer reaction product of residual acid from the carbonizingprocess and at least one added fertilizer precursor.
 2. The fertilizerproduct of claim 1 wherein the residual acid comprises sulphuric acid,phosphoric acid, or both sulphuric and phosphoric acid.
 3. Thefertilizer product of claim 1 wherein the fertilizer reaction productcomprises one or more of ammonium sulphate, monoammonium phosphate,diammonium phosphate, ammonium nitrate, potassium sulphate, potassiumnitrate, potassium phosphate, potassium sulphite or potassium sulphide.4. The fertilizer product of claim 1 further comprising a micronutrient5. The fertilizer product of claim 4 wherein the micronutrient comprisesone or more of Mg, Cu, Zn, Fe, B, Mn, or Mo.
 6. The fertilizer productof claim 1, comprising a portion of immediately available fertilizerreaction product and a portion of carbon-bound slow-release fertilizerreaction product.
 7. An intermediate product for producing a fertilizerproduct, comprising: (a) an acid-carbonized microporous matrix derivedfrom expanded biomass, having an available pore volume; and (b) aresidual acid from the carbonizing process impregnated in the porevolume, in an amount less than 71% by weight of the intermediateproduct.
 8. The intermediate product of claim 13 wherein the residualacid is impregnated in the pore volume in a volume occupying less than80% of the available pore volume.
 9. The intermediate product of claim14 wherein the residual acid occupies less than about 70% of theavailable pore volume.
 10. The intermediate product of claim 15 whereinthe residual acid occupies than about 60% of the available pore volume.11. The intermediate product of claim 13 wherein the residual acid ispresent in an amount less than about 60% by weight.
 12. The intermediateproduct of claim 17 wherein the residual acid is present in an amountless than about 50% by weight.